Liquid crystal displays (LCDs) are widely used in electronic calculators, games, notebook computers and televisions. Liquid crystal displays are generally flat and light, can be driven by low voltages and can consume low power.
Referring now to FIG. 1, a cross-sectional view of a liquid crystal display is shown. As shown, the liquid crystal display includes a pair of liquid crystal display substrates, also referred to herein as upper and lower substrates 2 and 2' respectively. A common electrode 3 is included on the inner surface of the upper substrate 2 and a scanning electrode 3' is included in the inner surface of the lower substrate 2'. Polarizing plates 1 and 1' are included on the outer surfaces of the upper and lower substrates 2 and 2' respectively. Alignment layers 4 and 4' are also included on the common electrode 3 and the scanning electrode 3' respectively.
Continuing with the description of FIG. 1, spacers 6 are included between the alignment layers 4 and 4' so as to maintain the upper and lower substrates 2 and 2' in parallel with each other and spaced apart by a predetermined spacing. Liquid crystals 7 are contained between the substrates. A seal 5 maintains the liquid crystals between the substrates 2 and 2'.
FIG. 2 is a flow chart illustrating conventional methods for manufacturing liquid crystal displays. As shown in FIG. 1, at Step 10, the upper and lower substrates 2 and 2', including the electrodes 3 and 3', are cleaned. The cleaning can prevent the surfaces of the substrate from being contaminated. The cleaning Step 10 may include ultrasonic wave washing, high temperature drying and cooling. Alignment layers 4 and 4' are then formed at Step 12. In particular, a polyimide (PI) resin composition is coated on the surfaces of the substrates 2 and 2' to a thickness of about 600 .ANG.. Then, the solvent in the polyimide resin composition is evaporated by heating the substrates 2 and 2', to thereby harden the alignment layers 4 and 4'.
Then, at Step 14, a rubbing process is performed on the surfaces of the alignment layers 4 and 4'. The rubbing process allows liquid crystal molecules to be aligned in a uniform direction upon injection as described below.
At Step 16, a cleaning process is performed to remove particles that are generated during the rubbing Step 14. Spacers 6, having a diameter of about 5 .mu.m, are scattered on one of the substrates at Step 18. The spacers act to maintain a uniform distance when the upper and lower substrates are joined as described below. At Step 20, a sealing agent 5 is printed or otherwise formed on at least one of the substrates. The sealing agent may be formed by printing using a seal mask or a seal spacer.
Then, referring to Step 22, the upper and lower substrates 2 and 2' are joined and then uniformly pressed together at Step 24 to main a uniform cell gap. The seal 5 is then hardened by heating at Step 26.
Then, liquid crystals 7 are injected into the gap between the adjacent substrates 2 and 2' at Step 28. The liquid crystals may be injected by wetting one end of the substrates with the liquid crystals in a vacuum chamber and then releasing the vacuum to inject the liquid crystals into the gap between the upper and lower substrates through a liquid injection hole. Thus, the liquid crystal injection process utilizes the pressure difference between the inside and the outside of the LCD panel to inject the liquid crystals.
During injection of the liquid crystals in Step 28, the substrates may become separated from one another so that the separation distance between the panels is larger than the diameter of the spacers 7. Accordingly, the space between the two substrate may become nonuniform. In order to obtain a uniform spacing, the substrates are pressed together under a pressure of about 0.5 kg/cm.sup.2 at Step 30. Then, the injection hole through which the liquid crystal was injected is closed. Finally, the panel is cleaned at Step 32 and polarizing plates 1 and 1' are formed on the outer surfaces of the two substrates at Step 34.
As described above, conventional manufacturing of liquid crystal displays may be complicated because of the large number of processing steps that may be involved. Moreover, since pressure differences are used to inject liquid crystals, it is desirable for the chamber to be under high vacuum. The need to provide high vacuum may involve long pump-down times and may therefore slow the manufacturing process. Accordingly, due to the large number of steps and the high vacuum processing, the entire process may be lengthy.